ABSTRACT

The aim of this study was to compare the population structure of the invasive bivalve Isognomon bicolor in three different areas on the coast of Rio de Janeiro State and to verify its temporal variation. All the areas presented high densities, reaching more than 1000 live individuals per 100 cm2. The number of dead individuals and recruits was higher in Ilha do Brandão (Angra dos Reis) than in the other areas. The individuals sampled at Praia Vermelha (Rio de Janeiro) presented the highest maximum and mean sizes, compared to those found at Ilha do Brandão. In this area, vermetid molluscs are dominant and build a complex reef structure where only a few individuals of I. bicolor can really grow.

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This paper describes the epibiosis of Ostrea cf. puelchana on Callinectes exasperatus (Gerstaecker, 1856), both collected from the estuary of the Paraíba River, in the state of Paraíba, northeastern Brazil. The basibiont crab was captured using a trap installed in mangrove area at a depth of about 2 meters. The oyster was closely attached to the left side of dorsal carapace covering most of the epibranchial, mesobranchial and metabranchial regions. Possible advantages and disadvantages for both the epibiont and the basibiont are discussed. We believe that young O. cf. puelchana may avoid a variety of potential predators due to the considerable movement capacity of C. exasperatus and may also serve as a small protective shield for the basibiont. However, the oyster, which is a bivalve with an epifaunal lifestyle, is likely to be negatively affected, mainly due to burrowing activity of the crab. This is the first record of epibiosis between bivalves of the genus Ostrea Linnaeus, 1758 and crabs of the genus Callinectes Stimpson, 1860.

Vermetid reef building species play an important role as ecosystem engineers modifying the physical environment, creating microhabitats and affecting local hydro-sedimentary patterns. We explore the association of native vermetid reefs (Petaloconchus varians) with the invasive bivalves Isognomon bicolor and Leiosolenus aristatus. We also examined the different utilization of the reef habitat, since L. aristatus is a boring species, comparing their population structure on sheltered and exposed rocky shores. Ten sites (five sheltered, five exposed) were sampled at Ilha Grande Bay (Rio de Janeiro, Brazil). I. bicolor and L. aristatus were the most frequent with mean densities of 20,000 (±3400) and 2100 (±600) ind.m2, respectively. There were no significant differences (t = 1.41; p = 0.17) between sheltered and exposed sites in relation to the densities of I. bicolor. However, there were significant differences (t = 3.14; p = 0.03) in relation to the densities of L. aristatus, with higher values at exposed sites. Mean size of both species was significantly (p < 0.01) higher in sheltered areas where the vermetid weight was significantly higher (t = 2.36; p = 0.02). Although native vermetid reefs act as a shelter for both invasive bivalves on sheltered and exposed rocky shores, they prevent the growth of I. bicolor which reaches smaller sizes in relation to populations outside of the reefs. Our results indicate that the two invasive bivalves might be differently affected by hydrodynamic processes.

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In many intertidal rocky shores at Ilha Grande Bay, state of Rio de Janeiro, Brazil, the vermetid gastropod Petaloconchus varians is the dominant organism, forming a well-developed and complex structure, where different groups of organisms live, including the invasive bivalve Myoforceps aristatus. The present paper describes the distribution and new record localities of M. aristatus at Ilha Grande Bay.